Neuroscientists from the University of Geneva have devised a technique that reveals evidence of cognitive decline prior to the onset of symptoms — an indication that deterioration in the brain happens before we're able to pick up on cognitive deficiencies.

Top image: Scans showing a comparison between a stable, healthy brain and one exhibiting cognitive impairment. The biggest difference is present between stable controls and mild cognitive impairment (MCI), indicated in red-yellow, notably in the posterior cingulate cortex. The comparison of stable versus deteriorating controls (blue) shows differences in the same region yet less pronounced. The comparison between deteriorating controls and MCI revealed no significant differences. (Image and caption credit: Haller/Radiology)

Early detection of cognitive decline is critical. Like so many other diseases, Alzheimer's is best treated in its early phases when interventions are at their most effective. Consequently, this new technique has the potential to serve as an important new tool in the very early diagnosis of preclinical dementia.

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What's more, it could compliment or replace other diagnostic methods, such as PET scanning, which can be quite invasive; patients are injected with fludeoxyglucose (18F) to help the machine form 2D or 3D images of the distribution of the contrast agent within the body. This allows neuroscientists to identify the markers of Alzheimer's disease in the brain and cerebrospinal fluid. Regrettably, the technique also exposes patients to radiation. An upgrade would certainly appear to be in order.

Measuring Brain Perfusion

A research team led by Sven Haller recently studied arterial spin labeling (ASL), a magnetic resonance imaging (MRI) technique that doesn't require the injection of a contrast agent. The method measures brain perfusion — the penetration of blood into tissue. ASL MRI is simple to perform and it doesn't require special equipment.

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For their study, which now appears in Radiology, the researchers looked at 148 healthy elderly participants and 65 people with mild cognitive impairment (MCI). All subjects underwent brain MRI and a neuropsychological assessment.

Brain perfusion. Red indicates low perfusion, yellow indicates high perfusion. Overall, the brain perfusion is similar between all three groups. The most prominent difference is present in the posterior cingulate cortex (indicated by the arrow), a region close to the midline in the superior and posterior part of the brain. Control participants who remain stable have higher perfusion as compared to deteriorating controls and MCI. (Image and caption: Haller/Radiology)

During the follow-up stage, the researchers discovered that, of the 148 healthy participants, 75 remained stable, while 73 deteriorated cognitively 18 months later.

Those who deteriorated exhibited reduced perfusions at their baseline ASL MRI exams, particularly in the posterior cingulate cortex, an area in the middle of the brain that's linked to the default mode network — the neural network that's active when the brain is not concentrating on a specific task. Patients with Alzheimer's disease tend to show pronounced declines in this area.

Signs of Decline

The pattern of reduced perfusion in the brains of healthy individuals who went on to develop cognitive deficits was similar to that of patients with MCI.

"There is a known close link between neural activity and brain perfusion in the posterior cingulate cortex," Dr. Haller said. "Less perfusion indicates decreased neural activity."

The results suggest that individuals with decreased perfusion detected with ASL MRI may temporarily maintain their cognitive status through the mobilization of their cognitive reserve, but will eventually develop subtle cognitive deficits.

Previous research done with positron emission tomography (PET), the current gold standard for brain metabolism imaging, found that patients with Alzheimer's disease had reduced metabolism in the same area of the brain where the perfusion abnormalities were found using ASL MRI. This points to a close link between brain metabolism and perfusion, according to Dr. Haller.

Super promising. Not only could ASL MRI be used as an early diagnostic tool, it's reaffirming our understanding of the physiological issues that underlie cognitive decline.